The invention relates to a pixel design for a display device, and more particularly, to a pixel structure and a method of repairing a defective pixel of a liquid crystal display device.
Generally, a liquid crystal display (LCD) controls light transmittance using an electric field to display an image. In order to attain this end, the LCD includes a liquid crystal panel having liquid crystal cells arranged in a matrix, and a driving circuit for driving the liquid crystal panel. The liquid crystal panel is provided with pixel electrodes and a common electrode for applying an electric field to each liquid crystal cell. With regard to a TN (Twisted Nematic) mode LCD, the pixel electrode is provided on a lower substrate (also referred to as a TFT (thin film transistor) array substrate which substantially consists of a transparent substrate comprising a plurality of TFTs arranged in an array) for each liquid crystal cell, whereas the common electrode is integrally formed on the entire surface of an upper substrate. With regard to an IPS (In-Plane Switching) mode LCD, the pixel and common electrodes with an interlaced-comb structure are formed on the lower substrate. The lower substrate comprises gate, data and common lines thereon. The detailed structure of the IPS-LCD is disclosed in, for example, U.S. Pat. Nos. 6,259,502 and 6,506,617, and therefore is not described here again. In any LCD, pixel regions are defined by crossing gate and data lines. Each pixel electrode is connected to a TFT serving as a switching device. The pixel electrode drives the liquid crystal cell, along with the common electrode, in accordance with a data signal applied via the TFT.
In order to achieve higher brightness and resolution, HAR (high aperture ratio) and COA (color filter on array) techniques have been widely employed. These methods generally form a thick organic insulating layer with a thickness of 1˜4 μm overlying the lower substrate (i.e. the array substrate). During formation of a contact hole with a high aspect ratio in the thick organic insulating layer, organic matter (e.g. polymer residue) is typically remains therein. This prevents pixel electrodes manufactured in subsequent processes from electrically connecting to the TFT, resulting defective pixel.
Current means of repairing defective pixels connects the pixel electrode to the TFT of the previous pixel, causing the repaired pixel to display the same color as the previous pixel. This method is disclosed in, for example, U.S. Application Publication No. 2002/0163602. Another repair method, known as the dark point repair technique, directly connects the pixel electrode to the data line or the common line, causing the defective pixel to display black or gray. Conventional techniques, however, cannot restore the original color of the defective pixel, thus suffers display quality.